LECTURE XI. 329 



they refer to liuman remains of a considerably more recent 

 date than the stone hatchets and the jaw of Amiens^ or the 

 skulls of the Belgian caves. 



One of these calculations is founded on the Delta of the 

 Mississippi. The alluvial deposits must have been continued 

 for an indefinite period ; for near New-Orleans, at a depth of 

 six hundred feet, the bottom of the deposits had not been 

 reached. The plain on which New Orleans stands rises only 

 nine feet above the level of the sea, and the excavations made 

 pass far below the sea level. In these excavations are seen 

 superimposed beds of cypress forests (Taxodmm distichumj. 

 On laying the foundations for the gas-works, the Irish navvies 

 had to give up the task, as they had to dig out wood instead 

 of soil. They were replaced by woodcutters from Kentucky, 

 who cut their way down through four superimposed layers. 

 The lowest was so old, that the wood cut like cheese. The 

 section of the banks also showed sunken forests, whilst stately 

 live oaks grew upon the banks, indicating that the surface had 

 not changed for years. 



In that part of Louisiana where the water-height presents 

 greater differences than in New-Orleans, Dickeson and Brown 

 have traced ten distinct cypress forests at different levels below 

 the present surface. These groups of trees, the live-oaks on 

 the banks, and the successive cypress forests, are superimposed 

 upon each other, as may be seen in many places in the vicinity 

 of New Orleans. 



Dr. Bennet Dowler has made an interesting computation as 

 regards the emergence of New-Orleans, in which these cypress 

 forests play an important part. He divides the history of this 

 event into three epochs : 



" 1 . The era of colossal grasses and waving prairies, as seen 

 in the lagoons, lakes, and the sea coast. 



2. The era of the cypress basins. 



3. The era of the present hve-oak bank." 



Many districts on the Mississippi show that the development 

 from the water proceeds in the order named. First appear the 

 grasses, then the cypress, and finally the live-oak. Assuming 

 an elevation of five inches in a century (the rate of the Nile 





